Selective solvent treatment of liquid hydrocarbon mixtures for segregation of contained aromatics



Patented July 6, 1948 sELEc'rrvE soLvENT TREATMENT or* LIQUIDHYDROCARBON FOR SEGREGATION AROMATICS MIXTURES OF CONTAINED Allen S.Smith, Ann Arbor, Mich., assignor to Blaw-Knox Company, Pittsburgh, Pa.,a corporation of New Jersey Application January 20, 1944, Serial No.518,964

51 Claims.

This invention relates to selective solvent treatment of liquidhydrocarbon mixtures for segregation of contained aromatics; and itrelates more particularly to continuous countercurrent selective solventtreatment of mineral oils and mineral oil fractions, especially naturalor cracked petroleum distillates, having a substantial content ofaromatic hydrocarbons, effected in such manner as to extract most ofsuch aromatic content therefrom in concentrated form.

It has long been known that petroleum or petroleum distillates could 'beseparated by various selective solvent extraction methods into 1) a moreparafllnic fraction, called the raffinate, containing relatively littlesolvent, and (2) a more aromatic fraction, called the extract or extractsolution, also containing a substantial proportion of the non-aromatichydrocarbons present in the original stock treated, together with mostof the solvent employed. Lubricating oil stocks have been thus refinedto free them of aromatic and asphaltic contaminants. There have alsobeen proposals to utilize the principles of selective solvent extractionfor improving motor fuel distillates of the gasoline type in respect toantiand other mineral oil fractions that are rich in aromatics,including cracked naphthas and the like, by selective solvent extractionIwith solvents selective for aromatics, for the specific purpose ofseparating therefrom valuable aromatic components in form suitable forthe purpose, among others, of blending with gasoline to improve itsoctane rating.

However, it is well known that such previously proposed methodsaccomplish only a comparatively rough qualitative separation at best.The extracty although richer in aromatics (and naphthenes) than theoriginal stock, still contains parafiins; While the raffinate, althoughdefinitely more parafi'lnic than said stock, includes also a veryconsiderable pro-portion of the original aromatics content. Attempts tobetter the extraction of aromatics by increasing the operatingtemperature, in order thus to increase the solvent power ef theselective solvent employed, are of no avail, generally-speaking, becausethis ordinarily results, at the same time, in increasing its solventlpower for parains and other non-aromatics present, such as olefins andnaphthenes.

Recognizing the great desirability of devising some commerciallyfeasible way of applying selective solvent extraction principles to theproduction, from mineral oil materials of t'he character mentioned, ofvaluable'aromatics in highly concentrated form, and thusimportantlysupplementing the supply of suchhydrocarbons available from othersources, various attempts have been made to overcome the aforesaiddifficulties and objections. For example, a fairly recent proposal is toselectively solvent-treat the stock in liquid phase, next to separatethe resultant extract into several aromatic-rich fractions bydistillation, and finally to subject the individual fractions, while invapor phase, to further extraction with a high-boiling selectivesolvent. Aside from other objections to this procedure, the recoveryasserted for it is only from 50 to '70 per cent of the aromaticsoriginally present in the stock. Another and more recent suggestion isto subject aromatic stock to selective solvent extraction, using as theselective solvent a dihydric alcohol charac-terized by having at leasttwo ether groups, such as triethylene glycol or tetraethylene glycol.This method appears to be even more inefficient, the extract obtainedevidently containing only a relatively small proportion of the totalaromatic content of the stock.

From a consideration of these and other proposals, it is apparent thatattempts heretofore made to solve the problem leave much to be desired.Aside from their generally characteristic low recovery of aromatics,some of the prior proposals have been impractical because of-prohibitively high cost of the specific solvent employed or of itsrecovery for re-cycling, or because of other expensive operationalfeatures that rendered them uncommercial. So far as this applicant isaware, no commercially feasible selective lsolvent extraction method hasheretofore been devised which enables approximating substantiallycomplete recovery of valuable aromatic hydrocarbons in concentrated formfrom a mineral oil feed stock containing them.

The importance of finding a satisfactory solution of the problem isobvious in view of the wide variety of essential purposes for whichbenzene, and its alkyl homologues such as toluene, Xylenes, mesitylene,cumene, etc., are greatly needed. Benzene is a raw material used innumerous syntheses of benzene derivatives as, for example, in themanufacture of such compounds as styrene and phenol. Toluene s thehydrocarbon raw material for the manufacture of high explosives, such astrinitrotoluene. The more highly alkylated aromatics are likewise usedin syntheses, but they are also used for blending purposes as additionsto motor fuel, particularly for production of aviation gasoline, inorder to improve the octane number and particularly the powercharacteristics of the fuel. Some of them, such as xylene, may serve asspecial reserve fuels employed directly, unblended, for temporary oremergency purposes, as where a plane is required under certainconditions to develop exceptionally high speed for a brief period. Inaddition, there is great need for a practical method of solventtreatinga mineral oil stock containing aromatics, in such manner as to recovertherefrom all or a high percentage of such aromatics content in the formof an extract product much enriched in aromatics, without necessarilyseparating individual aromatics as such. As examples of this may bementioned the production, by selectively extracting a gasoline feedstock having a low or medium octane number, of an extract richer inaromatics than the gasoline feed stock and consequently higher in octanenumber; as well as the production of high solvency naphthas from feedstock of lower solvent power.

` Accordingly, it is a primary object of the present invention toprovide an efficient and industrially practicable selective solventextraction process whereby a high proportion, commonly 90 to 95 per centand frequently as much as 98 to 99 per cent, of the valuable aromatichydrocarbons present in. mineral oil charging stocks or feed mixtures ofvarious specific kinds can be recovered in the form of products which,while still containing non-aromatics in proportion which may varywidely, are commercially valuable products for various purposes. Afurther and more specific object is to provide such a process wherebythe hydrocarbon components of the stock or feed mixture may be separatedinto an aromatic portion or extract exceptionally low in paralns andnaphthenes, and a parafllnic portion or rafllnate substantially freefrom aromat-i'cs and containing nearly al1 the paraffns and naphthenesinitially present in the stock. A further object of the invention is toaccomplish the foregoing in a relatively simple and economica-l manner,in a continuously operating system, at ord-lnary temperatures, that is,within a normal temperature range of, say, 70 to 90 F., and withtemperatures of 60 and 100 as extreme limits in practice. Other objectsof the invention will appear in connection with the further detaileddescription of the invention to be given hereinafter.

Liquid mineral oil charging stocks or feed mixtures adapted to beprocessed in accordance with the invention are of wide variety,obtainable from many different sources. In general, however, they areessentially complex liquid mixtures or solutions of hydrocarbons botharomatic and nonaromatic, .the latter frequently including naphthenesand olens in addition to paraiiins. Examples of suitable stocks aregasolines, naphthas, burning oils, or similar fractions derived fromcrude petroleum by straight-run distillation; corresponding or otherdist-illates produced by the thermal decomposition or cracking ofpetroleum or other mineral oils, or cuts therefrom; as well as fractionsseparated from cracked distillates, light oils, or the like. Light oilsare fractional distillates from coal-tar consisting of mixtures ofbenzene, pyridine, toluene, xylene, phenol and cresols. Thelower-boiling fractions separated from crude petroleums, such asgasolines, naphthas and burning oils, when produced alcohol, ethylalcohol, isopropyl alcohol, diproby straight-run or non-crackingdistillation, are

composed mainly of parains, naphthenes, and

aromatics. Olein hydrocarbons are normally presen-t in relativelynegligible proportion, if at all. On the other hand. the lower-boilingdistillates produced through reactions of thermal decomposition andpolymerization, that is.

l through the use of processes known broadly in be termed its generalmechanics of operation, i is in the main already well known. 'I'hat isto say.

the solvent is lintroduced into the column at one end of the extractionzone, the liquid feed is introduced at a location intermediate the endsof the column, and extract solution comprising nearly all of the solventtogether with the extracted hydrocarbons dissolved therein, is removedat or near 'the other end of the extraction zone; while a solvent-poorliquid raillnalte comprising the undissolved hydrocarbons leaves thecolumn at a point near where the solvent is introduced.

In accordance with the present invention, however, the solvent employedis a composite or mixed solvent of a particular type not heretoforeemployed, it is believed, which has been found to be outstandinglyeffective for the purposes hereinabove stated, and which is alsobelieved to be novel 40 as a composition. Such novel type of mixedsolvent comprises two component solvents now to be identified. Both arealiphatic oxygenated polar compounds. One of them, which may be termedthe primary solvent, or the primary component of the mixed solvent, must=be atl least partially miscible with the hydrocarbon mixture as a wholethat is to be solvent-treated, and must also be selective for thearomatic component or content of that mixture. 'I'he primary solventmust contain at least one hydroxyl group in the molecule; andk it maycontain two or more hydroxyl groups,

` in which latter case it musty also contain at least one ether group.With respect to the other component solvent, which may be termed themodifying, auxiliary or secondary solvent, the essential requirementsare that it shall be completely miscible with the primary solvenrt butonly partially miscible, at most, with each of the components (aromaticand non-aromatic) of said hydro'carbon mixture; also that it shallcontain at i least two hydroxyl groups in the molecule, accompanied ornot either by one or more ether groups or else by nitrogen. In respectto both solvents,

it is to be understood that the above specified requirements formiscibility apply to operating temperatures within the range at whichthe extraction is to be conducted.

Within the foregoing denitions of the primary and secondary solvents tobe used in mixture in accordance with the principles of the invention,it is found that particularly desirable results are obtainable,especially when operating at from 70 to 90 F., if the primary solvent`is selected from the group consisting of methyl pylene glycol,tetraethylene glycol, hexaethylene glycol, nonaethylene glycol and aproduct available under the trade name Carbowax 1500, which is acommercial mixture of glycols having a molecular weight of about 1500and a melting point of about 3 537 C.; and if the secondary solvent isselected from the group consisting of ethylene glycol, diethyleneglycol, triethylene glycol, tetraethylene glycol, propylene glycol, andtriethanolamine.

It will be noted that tetraethylene glycol is included both as a primarysolventV and as a secondary solvent in the two groups of solvents justspecifically designated hereinabove. This exemplifies the occasionalinstance where, within the scope of the invention in its broaderaspects, a solvent compound can be employed in either capacity, subjectto certain limitations. If tetraethylene glycol is used as a primarysolvent, only a very small amount of secondary solvent (e. g., ethyleneglycol) can be tolerated in mixture therewith; if used as a secondarysolvent, a large amount of it must be added to the primary solvent (e.g.. dipropylene glycol) to provide a mixture suitable for practicing theinvention. For the purposes of the invention, tetraethylene glycol isuseful chiefly as a secondary solvent. The commercially available formof tetraethylene glycol known as Polyethylene Glycol 200 may beemployed. Because of its physical properties. triethanolamine is lessdesirable as a secondary solvent, generally speaking, than a glycol.

In actual practice of the invention, it has been found usually mostdesirable that both the primary and secondary solvents shall bealcohols, with the secondary solvent a dihydric alcohol. Morespecifically, use of a m-ixed solvent in which both the primary andsecondary solvents are glycols, and especially one consisting ofdipropylene glycol as the primary solvent and ethylene glycol as thesecondary solvent, has outstanding adv-antages in some of the mostimportant practical applications of the new process. In addition to theglycols that have been specifically referred to, there are also otherglycols suitable for use either vas primary or secondary solvents in asolvent mixture to be used in practicing the invention, including otherpropylene glycols, as well as methylene glycols and butylene glycols.

Relatively slight miscibility of the secondary solvent with botharomatics and non-aromatics is a practical advantage. It is highlydesirable also that such solvent action as the'secondary solvent exertsshall be selective for the aromatic hydrocarbons, although, in thebroader aspects of the invention, this is not an indispensablecharacteristic. Ethylene glycol and propylene glycol are found to beespecially satisfactory in this respect.

While either the primary solvent or the secondary solvent may itselfconsist of more than one member of the indicated group of compounds towhich it belongs, practice of the invention is simpler and generallymore satisfactory where each consists of but one such member,

It has been found that, by making use of a mixed solvent consistingv ofprimary and secondary components of the types herein designated, theselective solvent extraction of valuable aromatics from mineral oil feedstock, which has heretofore been commercially impracticable because ofexcessive cost of plant and operation or for other reasons, can becarried out with such 6 efllciency and economy as to be commerciallyfeasible.

.The proportionlng of the components of the mixed solvent must be soadjusted that this composite solvent and the liquid mixture or solutionof hydrocarbons constituting the feed stock are only partially misciblewith each other, with the result that, at the operating temperature,they form in the extraction column two distinct liquid phases, thesolvent or extract phase and the hydrocarbon phase; the composition ofeach phase varying, of' course, as it progresses from one level toanother in the column, corresponding to different stages of theextraction. More specically, the mixed solvent components must bepresent in such ratio that two separate liquid phases are formed uponmixing the composite solvent with the most soluble aromatic component tobe extracted. It is essential to the practical operation of the systemthat there be suflicient difference in density between the solvent phaseand the hydrocarbon phase, at all points in the column, to causeeffective counterow of the two phases throughout the extraction zone aswell as adequate separation of the phases in suitable settling zonesfrom which raffinate and extract, respectively, are removed; and thisrequirement is readily met when using a'mixed solvent of the type hereindisclosed.

Employment of a mixed solvent of the character specified enables notablyhigh recovery, as an aromatic-rich extract, of the total aromaticscontent of a mineral oil feed, without carrying the extraction beyondwhat, by analogy to distillation, may be termed a stripping operation;and such practice is within the scope of the invention, broadlyconsidered. However, much higher concentration of the aromatics and muchmore complete separation therefrom of paraflins and naphthenes iseffected if the aromatic-rich product obtained in the strippingoperation is subjected to rectification by counter-current contact witha, highly aromatic reflux. In its most desirable practical embodiments,therefore, the invention is characterized by inclusion of this furthertreatment, with resultant production of an extract representing not onlyan exceptionally high recovery of the aromatics present in the feed, butalso a more complete separation therefrom of parafiins and naphthenesthan has been attainable by prior methods. Also. if the feed containsoleflns and diolens, the proportion of these hydrocarbons remaining inthe extract may be considerably reduced by the rectifying operation.Although it is not broadly new to employ a reflux in selective solventcountercurrent extraction, the use thereof in the recovery of valuablearomatics from a mineral oil feed stock containing them is new, so faras this applicant is aware, particularly in the manner and proceduralcombination herein disclosed.

In order to explain further the principles of the invention, certainpractical embodiments thereof will be hereinafter described in detail byway of specific illustrative example, but without implying limitation ofthe invention to those particular embodiments or to the specificdetailsl thereof.

One important typical practical application of the invention consists inemploying it for the selective solvent extraction of a mineral oil fee-istock containing a. more or less wide series or range of aromaticcompounds, for production of an extract which contains either the entireseries aforesaid or a desired portion thereof, in amount representing arecovery of 85 to 90 per cent. or better, of the total amount of thecorresponding `aromatic compounds originally present in the feed stock,and at relatively high concentration. For example, assume that the feedstock is a whole cracked gasoline analyzing, approximately, 29% aromaticcompounds, substantially all in the Cv--Cw range (i..e., toluene andhigher benzene homologues),.and 71% non-aromatics; this tot-alpercentage of non-aromatics consisting of olens and 42% parafilns plusnaphthenes, in the Cv-Cw range, and 14% non-aromatics below C7 and aboveCm. Assume further that the extraction is to be carried out at operatingtemperatures between 70 and 90 F. Assume also that the mixed solvent tobe used is a mixture consisting of dipropylene glycol as the primarysolvent and ethylene glycol as the secondary solvent.

Although it is feasible to vary considerably the proportioning of theprimary and secondary components of the mixed solvent in any mixture of`the solvents herein designated as suitable, while in all casesrealizing the benets of the invention in at least substantial degree,practical considerations usually render optimum a. certain particularproportioning of the specific component solvents employed in anyinstance for extraction of a given type of mineral oil feed within agiven temperature range. Thus, where the mineral oil feed to besolvent-treated is comparable in general character to the whole gasolineof the present the toluene and higher homologues; whereas, if

the proportion of ethylene glycol be materially less than 35%, a mixtureof the composite solvent with benzene produces but VY'one homogeneousphase,with no separation of a benzene-rich phase. Neverthelessconsiderable latitude is permissible in this respect. In general, theproportioning of the mixed solvent may, for practical purposes, rangefrom 25% dipropylene glycol and r15% ethylene glycol as one limit, to80% dipropylene glycol and 20% ethylene glycol as the other; nor is itto be understood that operability of the process is confined strictly tothis stated range. But better results are usually obtainable by stayingwithin it. The factor of viscosity also has to be considered inproportioning the mixed solvent, especially when the operatingtemperature is relatively low.

' Among the advantages of using a mixed solvent of the characterdescribed, whatever specic type of mineral oil feed is being extracted,are the following: Each of the component solvents is miscible to only avery limited extent with paraf fins and naphthenes. Thus, in thespeciilc mixed solvent used in this illustrative example, thedipropylene glycol is miscible in all proportions with the typicalaromatic (toluene); while the ethylene glycol is only somewhat moremiscible with' the aromatics than with parafllns and naphthenes. Themixed solvent is almost completely immiscible with parafllns andnaphthenes, and only partially miscible with the most solublehydrocarbon component of the feed, but is selective for aromatics. Inusing the mixed solvent to extract a solution of mixed hydrocarbons,therei'ore, two immiscible phases coexist, which phases are of widelydiffering densities anu nence capable of separating quickly in asuitable settling zone. The boiling points of the glycols, as well asthat ot triethanolamine, are much higher than those of the dissolvedhydrocarbons, thereby permitting ready separation and recovery of theextracted material by distilling it from t? le extract solution, leavingvirtually all the mixed solvent, which is stable at the distillingtemperatures involved, for re-use incycle. Furthermore, the readysolubility of the mixed solvent in water renders very simple the removaland recov- K ery of the small amount contained in th'e extractdistillate, as well as the still smaller amount carried out of theextraction zone by the raffinate.

The presence of more than a relatively very small proportion of water inthe mixed solvents employed in practicing the invention reduces theirsolvent. power for aromatics to an extent that is undesirable orexcessive, and is accordingly to be avoided so far as is practicable.Therefore, since small amounts of water, including th'at normallycontained in the feed (a few hundredths of one per cent), unavoidablyenter the extraction system from various sources and contaminate thesolvent, although in a single passage of the solvent through the systemsuch contamination does not occur to a degree that cannot be toleratedcommercially, it is desirable that the solvent, at the point where it isintroduced into th'e system, be as nearly anhydrous as is practicable.However, if the water content of the mixed solvent, as introduced, doesnot materially exceed 1 per cent, the efficiency of the process remainsrelatively high and, for the purposes of this invention, is properly tobe regarded as carried out substantially in the absence of water;although it is much better practice, and entirely feasible as la rule,to keep well below this indicated maximum.

In extracting the aromatics from the above- 'described whole crackedgasoline in accordance with' the principles of the invention, using a65-35 mixture of dipropylene glycol and ethylene glycol, one desirabletype of apparatus plant or system practical to employ is showndiagrammatically in the accompanying drawing, which is largely in theform of a simplified flow-sheet. It is to be understood that, in orderto avoid unnecessarily complicating the drawing and description,numerous parts and accessories such as pumps, valves, thermostatic andother types of automatic 4level and ilow controls or regulators, heatexchangers, coolers, vapor-liquid separators, auxiliary tanks, and thelike, which' are commonly employed in systems of this general characteras is well understood by those skilled in the art, and which areactually included in the system as employed in practicing the novelprocess, are not here illustrated. s

Referring to the drawing, the extraction column I0 comprises upper andlower packed sections I I and I2, the packing material employed in thesesections being of any suitable type that will provide a relatively largecontacting surface such', for example, as Raschig rings or Berl saddles.The solvent is pumped into the extraction column from solvent storagetank I3 through line Il, entering the column at a level just above upperpacked section il. Although, in this instance, the solvent is toconstitute the continuous phase and the feed the discontinuous ordisperse In the present example, the solvent fills the void space aroundthe packing, flowing downwardly as a continuous liquid phase. The wholegasoline constituting the feed, containing about 29% aromatics, ispumped from storage tank I through line I6 into the column at anintermediate point, substantially the midpoint in this instance,immediately below the aforesaid upper packed section II and above thelower packed section I2. The respective rates at which the gasoline feedand solvent enter the column are so coordinated and controlled as tomaintain a suitable predetermined ratio between them. In the presentinstance the volume ratio of solvent to feed is 4.7 to l. The feed is sointroduced into the column as to cause it to be dispersed in finedroplets uniformly distributed over the whole cross sectional area ofthe column. Various devices for effecting such dispersal, any oi whichmay be employed in practicing this invention, are well known in the artand therefore none requires specific description here. Being of muchlower A specific gravity than the solvent, the feed thus dispersed asdroplets rises through the packed section, flowing countercurrently tothe descending solvent introduced above the packed section II. In thisway a large interface, at which the mixed hydrocarbons of the gasolineare in intimate contact with the mixed solvent, is produced. By thisprocess of the counterilow of the ascending hydrocarbon phase and`descending solvent phase, opportunity is afforded at each point for amutual interchange of material between the two phases.

As the gasoline feed material enters the column and is dispersed incontact with the solvent phase, it loses hydrocarbons to the solventphase, but preferentially aromatic hydrocarbons rather than parains andnaphthenes. The equilibrium proportion of olefins also passes into thesolvent phase. As the hydrocarbon phase ascends through packed sectionII, it continues to lose hydrocarbons to the solvent phase,progressively, in the manner stated, so that, by the time it has reachedthe top of said section, it has lost all but a small part of itsaromatic hydrocarbons to the solvent phase.

When the solvent or extract solution phase initially contacts theascending hydrocarbon phase at the top of the packed section,hydrocarbons from the hydrocarbon phase dissolve into the solvent and anextremely small amount of solvent dissolves into the hydrocarbon phase.As the solvent phase descends the upper section of the column, itbecomes progressively richer in its constituted the continuous phase andthe solvent the disperse phase, as is practicable, the interface mlgdhtbe maintained in a settling zone below the fee f The raffinate, poor inaromatics and containing only a very small proportion of the solvent,typically on the order of 0.25% by weight, leaves the top of the columnthrough line I9; while the extract phase, when it arrives at the feedlevel in its downward flow, is rich in aromatics.

By the countercurrent contacting operation thus far described, which, aspreviously stated, may be called a stripping treatment, removal ofnearly all the aromatic hydrocarbons from the feed material can beeffected, and a raillnate prowhich turbulence of the two liquid phasesbecontent of aromatic hydrocarbons, while at the aromatic hydrocarbons.

At any desired predetermined level in the lcolumn suitably distant fromthe feed inlet, an interface is established between the lighterrailinate solution and the heavier solvent phase, in order to permitseparation of one phase from the other. The predetermined level of thisinterface is maintained constant by properly coordinating the rates atwhich the several liquids enter and leave the column. In the presentinstance this separation interface, indicated at I1, is located near theupper end of the extraction column in settling zone I8, and may bemaintained constantly at this level by appropriate constantlevel meansacting automatically to control the rate at which aromatic extractsolution is led from the column. If the hydrocarbon feed stock comes sogreat as to prevent proper counterow thereof. Concentration, in theextract solution leaving the base of the upper packed section II. offrom to 95 per cent or more of the total aromatics contained in thegasoline feed stock is readily attainable in practice. As has alreadybeen pointed out, this extract solution also contains a, minorproportion of the paralns and naphthenes that were contained in thefeed, as well as some olens.

If, as is contemplated by the invention in its broader aspects, theaforesaid extract solution obtained in the stripping operation iswithdrawn from the column at this stage without being subjected to thehereinafter described further countercurrent contacting treatment in thenature of rectification, and is freed of solvent, the resultant extractconstitutes a product useful and valuable in itself for variouspurposes. It consists largely of aromatic hydrocarbons which are in theCfz-Ciu range for the most part, together with lesser proportions ofparafllns, naphthenes and oleflns. It represents, moreover, a morenearly complete separation of aromatics from a feed of the general typehereinvolved than has been achieved, so far as this applicant is aware,in any commercially feasible solvent extraction process heretoforeproposed.

However, a product much more concentrated in respect to aromatics can beobtained by subjecting the product of the stripping operation to suchrectifying treatment, in the lower packed section I2 of the extractioncolumn, whereby to reduce its content of paraiiins and naphthenesespecially. Such rectifying treatment therefore constitutes an importantpart of the novel process where such a more concentrated extract productis desired.

By this further treatment 0f the intermediate extract solution, removallof lmost of its content of p-arafns and naphthenes, together with asubstantial part oi its content of oleiins, can be accomplished. Theextract solution continues to descend through the column, constituting acontinuous liquid phase filling the voids in the mass of packingmaterial in said lower or rectifying section I2. It travels downwardcountercurrent to and in intimate contact with an ascendingdiscontinuous phase formed by dispersed droplets of an aromatic liquidreflux introduced into the column through line at a point just below thelower packed section I2, and there dispersed as line droplets in thesame general manner as is the feed material introduced through line I6.Said liquid reflux contains aromatic hydrocarbons in higherconcentration than does the extract solution phase leaving the base ofthe lower packed section I2. More specifically, this reflux liquidconsists in this instance of a suitable quantity of the aromatic extractproduct obtained by removing most of the mixed glycol solvent from saidextract solution phase at a later stage of the complete process, as willmore fully appear hereinafter. In other words it comprises the samemixture of hydrocarbons contained in said extract solution phase, in thesame relative proportions, but is substantially undiluted with solvent.Since it has a much lower specific gravity (0.85 e. g.) than saidextract solution or solvent phase, the dispersed droplets of thisaromatic reux rise through and in intimate contact with such downwardlyflowing solvent or extract phase. As the latter descends, it becomesprogressively richer in aromatlcs dissolved from the reiiux phase; alsopoorer in paraflins and naphthenes and, in some degree, poorer inolefins, dissolved from it by and into the reiiux phase. The refluxphase, in turn, .becomes progressively richer in parafiins, naphthenesand olefins, while at the same time becoming progressively poorer inaromatics. By the time it leaves the top of the lower packed section I2,the composition of the reflux phase has become substantially the same,in respect to content of arom-atics, as that lof the feed material, withwhich it merges to constitute the disperse hydrocarbon phase ascendingthrough the stripping section.

At the |base of the column, a settling zone 2| is provided in order topermit gravity separation of any entrained droplets of reflux from theiinal extract solution. The iinal extract solution, saturated at theoperating temperature with hydrocarbons, mainly aromatic, flows from thebase of the column through line 22. Freeing this extract solution ofsolvent in the manner to .be presently described gives a finishedextract product which,`

even when operating with a column having a relatively short strippingsection, regularly represents a recovery of at least 90% to 92% of thetotal amount of aromatic hydrocarbons in the feed stock. Thus, whenconducting the extraction of the gasoline stock specifically describedhereinabove in a iO-foot column having a 12-foot stripping section,operating within a temperature range of 70-90 F. lwith a feed of 86.3gallons per minute, ya solvent ratio of 4.7 to 1, and a re.

ux of 71.8 gallons per minute, approximately 92% of the aromatics of thefeed are recovered in a finished extract product analyzing approximately66% aromatics, 7% parafilns and naphthenes taken together, and 9%oleiins, all in the C'z--Cio range; together with 18% non-aromatics inthe ranges below C1 and above Cio.

Assuming. by way of example, employment of a column such ,as thatillustrated in the drawing. having an upper packed section I I that is6.5 feet in diameter and 27 feet high, anda lower packed section that is8 feet in diameter and 15 feet high, a recovery of materially betterthan 92% of the aromatic hydrocarbons of that same gasolinefeed stockAcan be achieved under operating conditions otherwise substantially thesame, as those just mentioned. By employing a longer rectifying i2section, separation of paramns and naphthenes from the aromatic extractcan be effected to virtually any desired extent, as well as some furtherseparation of olefins.

It will be seen that, as a result of the complete countercurrentselective solvent extraction and rectification procedure hereinabovedescribed, not only has there been accomplished the substantiallycomplete separation or recovery from the feed material of nearly all itsentire content of aromatic hydrocarbonswhich separation is achieved inthe upper or stripping packed section II--but in addition the extractsolution or phase containing the separated aromatic hydrocarbons hasbeen concentrated with respect to its aromatic hydrocarbon content,while its content of other hydrocarbons has been reduced to apredeterminble extent, in what amounts to a rectii'ying treatment in thelowerpacked section I2 of the' column. Subject only to practicallimitations of extraction column design, and of the ratio betweensolvent and feed, and ratio of reflux to end product, the proportion ofparaiilnic and naphthenic hydrocarbons contained in the extract solutionleaving the extraction column can be reduced by this procedure tovirtually any desired minimum. For example, it is often enti-relypractical, in carrying out the process of the invention, to produce anextract solution in which the content of the paraiiinic and naphthenichydrocarbons combined amounts to only 5% or even somewhat less -of theentire hydrocarbon content, by Weight. In such case, the aromatic reiiuxintroduced into the lower end of thelower packed section :must of coursecontain only such low percentage of paraflinic and naphthenichydrocarbons. Where, as is often the case, it is permissible that theproportion of parafiinic and naphthenic hydrocarbons in the finishedextract be 10%, for example, the aromatic reflux will be characterizedby that same percentage content of paraiiinic and naphthenichydrocarbons.

It is not feasible in practice, however, to reduce the content ofolefinic hydrocarbons to a similar extent by the described procedure.This is because of the fact that the equilibrium conditions between the-mixed glycol solvent, however proportioned, and the olefins of thefeed, are such that it is not practicable to make a clean separation ofthe olens from the feed. The best that can be done, practically, is toeffect a distribution of the oleiins between ramnate and extract suchthat much the 'greater proportion goes into the raiiinate, saytwo-thirds or more, while the remainder goes into the extract.

Where it is desired to obtain a final aromatic product substantiallyfree of olefins, chemical treatment of the solvent-free aromatic extractwith 66 B. sulphuric acid in the well-known manner, followed byfractional distillation, vremoves the oleiin hydrocarbons substantiallycompletely.

In the complete process, the extract solution passing from the lowerpart of the extraction column is appropriately treated to separate thesolvent from the extracted matter. The separated solvent is recoveredand re-cycled, while a portion of the concentrated extract is also re.-turned to the column as reflux for the rectifying section. Mostdesirably, the rafiinate is likewise treated for solvent separation'.and recovery, notwithstanding the fact that it carries only a relativelyvery small proportion of the mixed glycol solvent out of the column. Inaccomplishing this separation and recovery, the separated solvent isalso freed from moisture to an extent ensuring that, when reintroducedinto the extraction column, it is substantially anhydrous in the sensethat it contains less, most desirably much less, than 1% of moisture.Furthermore, in the continuous re-use of the solvent, there is atendency for the solvent gradually to become contaminated withhigh-boiling substances dissolved from the hydrocarbon stock extracted,or formed from the solvent itself. An effective way to prevent theseimpurities, as well as the moisture content, from building up in therecycled solvent to an undesirable extent, is to divert a certainproportion of the solvent from the main stream of recovered solventbefore returning it to the column, and to distil the diverted portion ofsolvent in such manner as to leave the impurities as a higher-boilingresidue which is removed from the cycle. Accordingly, in its bestpractical embodiments, the novel process includes recovery andpurification of the solvent, most desirably by the procedure now to bedescribed.

After leaving the base of extraction column or tower l through line 22at a temperature of about 85 F. (e. g), the extract solution, containingthe extracted hydrocarbons at a concentration of around 16%, forexample, is suitably heated to 180 F. or higher, as by passing itthrough a heat exchanger, and is then delivered into vacuum distillationtower or evaporator 23 provided with plates or trays 24 of any suitabletype, at a level 25 intermediate the lower or stripping section 26 andthe upper or rectifying section 21 of said tower. The separatingdistillation accomplished in tower 23 is conducted under operatingconditions such that, as a iinal result, virtually all the extractedhydrocarbons, together with virtually all the moisture present and asmall proportion of the mixed glycols (e. g., 2%), are separated asoverhead vapors which are led from the top of the tower through vaporline 28; leaving as stripped bottoms nearly the whole of the mixedglycols solvent containing a minute proportion of hydrocarbons (e. g.,

Such a substantially clean separation of extract and moisture fromsolvent is readily attainable under proper operating conditions now tobe described. With the aid of suitable vacuum-producing means (notshown), such as a steam jet ejector, connected in the system in a mannerwell understood in the art, the distilling operation and thecondensation of the separated overhead vapors occur at low absolutepressure. Thus, a vapor pressure of about 85 millimeters mercuryabsolute is desirably maintained in the vapor space below the strippingsection 28 of the tower; which, employing a tower of typical design,means maintaining an absolute vapor pres- Asure of about 65 millimetersin the top of the tower. The liquid residuum or bottoms produced in thedistilling operation and having a temperature of about 300 F. leave thebase of the column through line 29 and pass to reboiler 30. The reboileris heated by closed steam coils 3|, the supply and return connectionsfor which are shown at 32, 33. The vapor space of the reboiler is atabout the same absolute pressure as that of the tower below section 26.Steam at 125 pounds gauge pressure (e. g.) is supplied to heating coils3l in such quantity that vapors of the mixed solvent are deliveredthrough vapor line 34 into the tower at a suiiicient rate to supply theheat units necessary to accomplish the desired stripping andfractionation in the column, the re- 14 quired amount of glycol-richliquid redux being introduced into the upper part of the tower throughline 35 from a source to be presently pointed out.

The extract solution delivered into tower 23 descends through the loweror stripping section thereof, being countercurrently contacted byascending hot vapors of the mixed glycols entering below said sectionfrom the reboiler and being thereby stripped of its hydrocarbon content,as well as of water. The resultant hydrocarbon vapors and water vapor,together with a small proportion of vapors oi the mixed glycols, ascendthrough the column and are fractionated in section 21 by countercurrentcontacting with the descending glycol-rich liquid reflux aforesaid. Thecomposition of the vapors leaving the top plate of the fractionatingsection is approximately 97 to 98% hydrocarbons (mostly aromatics),together with some solvent and water in the proportions givenhereinabove.

The vapor product leaving the top of column 23 passes through line 28 tocondenser 36, provided with cooling water intake and dischargeconnections 31, 38. Uncondensed vapor and gas are sucked away by thevacuum-producing means, while the condensate, at a temperature of, say,F., ows from the condenser through line 38 to decanter 40. There thecondensate separates into two layers of which the upper comprisespractically 99% of the condensate and consists of the hydrocarbonextract, wholly freed of the mixed solvent except for a minuteproportion, on the order of 0.1% by weight, dissolved therein. The lowerlayer consists principally of the mixed glycols but contains about 5% ofwater and 2% of hydrocarbons, by weight.

The nearly pure extract is decanted through line 4l into extractreceiver 42. From this receiver, the amount required to provide thearomatic reiiux for the rectifying section I2 of the extraction columnis pumped through line 28 at a properly controlled rate, and introducedbelow said section I2 as already described hereinabove. If the remainderof the extract is to be treated for removal of its very small content ofsolvent, it maybe passed from receiver 42 through line 43 to washer 44,entering at the base of the washer and passing upwardly therein throughsuitable packing or the like adapted to ensure thorough contacting withdown-flowing wash water introduced through line 45 into the upper partof the washer. From the top of the washer, the extract, washed free ofsolvent, is conducted through line 46 to finished extract storage 41.

The aqueous mixture of glycols constituting the lower liquid layer indecanter 40 is drawn of! through line 48, part of it going throughbranch line 35 to provide the glycol-rich liquid reux introduced intothe upper part of distillation tower 23, as previously described; whilethe rest is passed through branch line 49 to aqueous solvent storage 50,there to be accumulated for subsequent dehydrating treatment to bedescribed hereinafter.

The main body of mixed solvent, constituting the liquid residum orbottoms produced in the distillation tower 23, is withdrawn fromreboiler 30 through line 5l. Its temperature is approximately 300 F. orsomewhat higher. A small portion of the anhydrous solvent may bediverted, continuously or intermittently, through branch line 52 toimpure solvent storage 53, there to be accumulated for purification byremoval of higher-boiling components in a manner to be describedpresently. The remainder is returned through line 53a to solvent storagei3, after utilizing it in a suitable heat exchanger (not shown) topreheat extract solution that is being introduced into tower 23 fromextraction column i0, as described hereinabove, and then further coolingit in any convenient manner to the temperature, say 85 F., at which themixed solvent is to be introduced into extraction column I0.

Where, as in the present example, the small amountof mixed solventcontained in the railinate leaving the top of column i is to berecovered, the raffinate is conducted through line I9 to the lower partof washer 54, which is similar to washer 44. Through washer 54, therailinate ascends in countercurrent contact with wash water introducedinto theupper part of the water through line 55. Most desirably, thewater used for this washing is that which was used in washer 44 andwhich, therefore, already vcontains the mixed glycols solvent dissolvedfrom the distilled extract collected in decanter 40. Accordingly, line55 is here shown as connected to the base `oi washer 44 and conductingused wash water therefrom for re-use in washer 54. Solvent-freerailinate leaves the top of washer 54 through line 55a which conducts itto .raffinate storage 55. Wash water carrying the mixed glycols pickedup in washers 44 and 54 leaves the base of washer 54 through line 51, bywhich it is delivered to aqueous solvent storage 50.

Suitable distilling means are provided for separating water from theaqueous mixed solvent collected in storage 50, and for separatinghighboiling impurities from thev anhydrous mixed solvent in storage 53.In the present example, a single distillation unit is employed for thesepurposes, the aqueous and non-aqueous bodies of solvent to be purifiedbeing handled separately therein, of course, and under differentoperating conditions. The distillation unit is here shown in simplifiedconventional form as a batch still comprising still pot 58 and platecolumn 59. The still pot is heated by closed steam coils 50, havinghigh-pressure steam supply and return connections indicated at 6I, Sie.

In dehydrating aqueous mixed solvent, the charge is introduced into thestill from storage 50 through lines 62-53. The distillation system ismaintained under reduced pressure which may be, for example, about 1254millimeters mercury absolute at the top of column 59 and about 145millimeters in the vapor space of the still pot; the temperature in thelatter being, say, 300 F. The vapors leaving the top of thefractionating tower through vapor line 54 pass to water-cooled condenser55, yielding a condensate which is 98-99% 61. The dehydrated mixedsolvent, left as bot? toms, is run oif through line 68 and, after havingits temperature reduced to around 8 5 F. by passage through heatexchange and cooling means indicated generally at 69, is returned to thesolvent circuit byline 10 which is connected to main solvent line 53a.This returned solvent contains on the order of 0.5% water, typically;and the quantity thereof being small as compared to the whole body ofsol-vent sent back through line 53 to solvent storage i3, the watercontent of the mixed glycols solvent delivered through linel4 into theextraction column at no time exceeds a 16 small fraction of 1%, commonlycn the order of 0.1% or less, in normal operation of the process.

When using the distillation unit 58--59 to purify the impure anhydroussolvent collected'in storage 53, the impure solvent is charged into thestill through lines 1I-63. Since the mixed glycols solvent is to bedistilled overhead in this case, leaving the high-boiling impurities asresiduum, the distillation is conducted under higher degree of vacuumranging, say, from 65 millimeters absolute at the top of column to 85millimeters in the still pot. The resultant mixed glycols condensate isreturned through line 12 to main solvent circuit line 53.; while theresiduum, consisting of the separated high-boiling impurities, may bedischarged to waste through line 13.

It will be understood that the extracting and rectifying operation inthe extraction column iii is continuous, as is also most desirably, thethe primary or principal separation and recovery of solvent which isperformed in distillation tower 23; flow of material through the variouslines being automatically controlled and coordinated in a mannergenerally well understood in the art. The operations of dehydrating andpurifying minor portions of the solvent, carried out in the distillingsystem 58-59, may also becontinuous to such extent as is desired.

The same procedure hereinabove described for treating a whole gasolinefor recovery of a wide range of valuable aromatics may be employed withgreat advantage in treating some particular fraction .thereof to obtainan extract predominantly rich in some one aromatic compound. Oneparticularly useful practical application of the invention consists insubjecting a Xylenerich fraction of a cracked gasoline or naphtha toselective solvent extraction with the hereinabove described mixed orcomposite solvent composed of dipropylene glycol and ethylene glycol,for production of a concentrated xylene product. Such a fraction isobtainable, for example, from certain commercially available gasolinesproduced by vapor-phase cracking. In a typical instance. such a gasolinecan be distilled into the following cuts:

Cuts or fractions: Percent by weight In a typical instance, the xyleneplus cut obtained in the vabove distillation has an approximate boilingrange of 250-350 F. and a specific gravity of 0.796, and contains about23% of Ca to Cio aromatic hydrocarbons by Weight. These aromatichydrocarbons are mostly xylenes (chiefly meta and para), together withsome cumene, ethyl toluene and mesitylene. The remainder of the cutconsists substantially of 60.6% parafflns plus naphthenes, and 16.4%olens.

Employing as solvent the same -35 mixture of dipropylene glycol andethylene glycol as before, and carrying out the process in the apparatussystem shown in the drawing and under the same conditions of operationalready described hereinabove, the rectified extract solution leavingthe base of the extraction column consists of about 84% mixed solventand 16% hydrocarbons. The hydrocarbon content analyzes, typically, about80% to 85% aromatics, 4% to 6% parafnns and naphthenes taken together,and the remainder substantially all oleilns. The ramnate, which containsa minor fraction of 1% of solvent, consists almost wholly (9B-99%) ofnon-aromatic hydrocarbons. The net result of the operation, in a typicalinstance, is a recovery, in the extract solution, of better than 95% ofthe aromatic hydrocarbons contained in the "xylene plus fractionconstituting the feed.

Where the production of a toluene-rich extract is desired, similarlygood results are obtainable by selective solvent extraction in the samemanner, with a mixed glycols solvent, of a toluene-rich feed such, forexample, as the 14.5% toluene cut distillable from the vaporphasecracked gasoline already mentioned. Such toluene cut may contain, in atypical instance, about 27% by weight of toluene, together withapproximately 29% of oleflns and 44% of parafns plus naphthenes; and itsspecific gravity is 0.79.

In another embodiment of the invention, the selective solvent may be amixture of methyl alcohol or methanol as the primary solvent withethylene glycol as the secondary solvent, the most desirableproportioning being '70% of the former to 30% of the latter, by weight.This specific mixture has a specific gravity of 0.875. Here also, themixed solvent, when introduced into the extraction system, should be asnearly anhydrous as is practicable, with a practical tolerance limit ofabout 1% for the moisture content. Use of this mixed solvent inaccordance with the invention, in place of a mixture of dipropyleneglycol and ethylene glycol, gives comparably high recovery of aromaticsfrom suitable feed stocks, and enables production of extracts alsocontaining the recovered aromatics at relatively high concentrations.Separation of` the mixed solvent from the extract and recovery of thesolvent components in proper condition for re-use in the process issomewhat less easy, however, because the low boiling point of methanolprecludes simply distilling olf the extracted hydrocarbons largely freefrom solvent, as in the case of the mixed glycols, and leavingpractically all the mixed solvents as bottoms.

Thus, assuming the above-mentioned 14.5% toluene cut obtained from acracked gasoline to be solvent treated in accordance with the invention,using the methanol-ethylene glycol solvent mixture aforesaid, separationof solvent from the toluene-rich extract is best accomplished in thefollowing manner. The extract solution passing from the base of thecolumn is subjected to a distilling operation whereby the methanol,together with enough of the toluene (with other extract hydrocarbons) toform the constant boiling mixture, is separated from the extractsolution as an overhead distillate product. The remaining toluene andother extract hydrocarbons, and the glycol, are left as still bottoms;and they form separate liquid phases becouse of their very limitedmiscibility. The toluene-rich layer may be decanted and returned to theextraction column as reflux; While the heavier glycol layer isseparately drawn o and subjected to dehydration and purification in thesame manner as has alreadyA been described for the mixed glycolssolvent.

The constant boiling mixture product composed of methanol and toluene iswashed with water to remove the methanol, yielding a solventfreetoluene-rich extract product. The water used to effect this washing maydeslrably have been previously used to extract the small amount ofsolvent (on the order of 0.02% ln this instance) carried out of theextraction column by the raffinate. In order to recover and concentratethe methanol, the methanol-water solution is subjected to distillationwith open steam in a suitable distilling column, in the known manner,for recovery of methanol of 99% or higher purity.

The separately recovered methanol and ethylene glycol are mixed inproper proportions to reconstitute the mixed solvent, and re-introducedinto the extraction column.

As further examples of speciiic mixed solvents that may be employed inpracticing the invention, the following are mentioned, the first solventnamed in each pair being the lprimary solvent: isopropyl alcohol andethylene glycol; isopropyl alcohol and propylene glycol; methyl alcohol(methanol) and propylene glycol, From experience thus far gained inactual use of the new process, however, the use of a mixture ofdipropylene glycol and ethylene glycol, as hereinabove described indetail, is at present believed to enable practical realization of thebenefits of the invention in greatest degree, and is accordinglyregarded as the best embodiment of the invention now known to thisapplicant.

What is claimed is.'

1. 'I'he process of extracting a valuable aromatic product from a liquidmixture of hydrocarbons that has both aromatic and non-aromaticcomponents, winch comprises intimately contacting such a hydrocarbonmixture in liquid phase with mixed primary and secondary liquid solventscomprising different aliphatic oxygenated polar carbon compounds, theprimary solvent compound being at least partially miscible with saidhydrocarbon mixture as a whole and selective for the aromatic componentof said mixture, and being selected from that group of such -compoundswhich consists of (1) compounds containing a single hydroxyl group inthe molecule and (2) compounds containing two hydroxyl groups and atleast one ether group in the molecule; while the secondary solventcompound is completely miscible with the primary but is only partiallymiscible, at most, with each of the components of said hydrocarbonmixture and contains at least two hydroxyl groups in the mole cule, saidoxygenated compounds being so proportioned in the mixed or compositesolvent that a mixture of the composite solvent with the most solublearomatic hydrocarbon to be extracted will separate into two liquidphases; separating the two liquid phases resulting from the intimatecontacting of said composite solvent with said liquid mixture ofhydrocarbons, namely, a rafnate phase poor in said aromatic componentand comprising most of said non-aromatic component, and a solvent orextract phase rich in said aromatic component, and removing solvent fromsaid extract phase to obtain an aromatic extract product; the extractionbeing performed substantially in the absence of water.

2. The process set forth in claim 1, wherein the primary solvent isselected from the group consisting of methyl alcohol, ethyl alcohol,isopropyl alcohol, dipropylene glycol, tetraethylene glycol,hexaethylene glycol, nonaethylene glycol, and Carbowax 1500, while thesecondary sol- '19 vent is a differentl solvent selected from the groupconsisting of ethylene glycol, diethylene glycol, triethylene glycol,tetraethylene glycol, and propylene glycol.

3. The process of extracting a valuable aromatic product from a liquidmixture of hydrocarbons that has both aromatic and non-aromatichydrocarbon components, which comprises intimately contacting such ahydrocarbon mixture with mixed primary and secondary solvents comprisingdiilerent aliphatic alcohols, the primary solvent being at leastpartially miscible with said hydrocarbon mixture as a whole andselective for said aromatic component, while the secondary solvent is adihydric alcohol that is completely miscible with the primary solventbut is only partialLv miscible, at most, with each of said hydrocarboncomponents, said alcohols being so proportioned in the mixed orcomposite solvent as to permit formation, at the temperature of opera-`tion, of separable liquid phases in a mixture of the composite solventwith the most soluble aromatic hydrocarbon to be extracted; separatingthe two phases resulting from such intimate contacting of thehydrocarbon mixture with the composite solvent, namely, a raflinatephase poor in said aromatic component and comprising most oi' saidnon-aromatic component, and a solvent or extract phase rich in saidaromatic compo-1 nent, and removing solvent from said extract phase toobtain an aromatic extract product.

4. The process set forth in claim 3, wherein the extraction' isperformed within the range of ordinary moderate atmospheric temperaturesand substantially in the absence of water.

5. 'I'he process set forth in claim 3, wherei the extraction isperformed within a temperature range of from about 70 to 90 F., and inthe substantial absence of water.

6. The process set forth in claim 3, wherein the primary solvent isselected from the group consisting of methyl alcohol, ethyl alcohol,isopropyl alcohol, dipropylene glycol, tetraethylene glycol,hexaethylene glycol, nonaethylene glycol and Carbowax 1500, while thesecondary solvent is a diiferent solvent selected from the groupconsisting of ethylene glycol, diethylene glycol, triethylene glycol,tetraethylene glycol, and propylene glycol. y

7. The process set forth in claim 3, wherein both the primary solventand the secondary solvent are glycols, and the extraction is performedwithin a temperature range of from about 70 to 90 F., and in thesubstantial absence of Water.

8'. 'I'he process set forth in claim 3, wherein the mixed solventconsists of dipropylene glycol and ethylene glycol.

9. The process set forth in claim 3, wherein the mixed solvent consistsof approximately 65% dipropylene glycol and 35% ethylene glycol, byweight.

10. The process set forth in claim 3, wherein the mixed solvent consistsof approximately 65% dipropylene glycol and 35% ethylene glycol, byweight, and the extraction is performed within a temperature range offrom about 70 to 90 F., substantially in the absence of water.

11. The process set forth in claim 3, wherein the mixed solventlconsists of methanol and ethyly ene glycol.

12. The process set forth in claim 3, wherein the mixed solvent consistsof approximately 70% methanol and 30% ethylene glycol, by weight.

13. Ihe process set forth in claim 3, wherein the mixed solvent consistsof approximately 70% zo l l methanol and ethylene glycol, by weight, anis substantially free of water, and the extraction is performed within atemperature range oi from about '10 to 90 F.

14. The process oi' extracting a valuable aromatic product from a liquidmixture of hydrocarbons that has both aromatic and non-aromaticcomponents, which comprises intimately contacting such a hydrocarbonmixture in liquid phase with mixed primary and secondary liquid solventscomprising diiferent aliphatic oxygenated polar carbon compounds. theprimary solvent compound being at least partially miscible with saidhydrocarbon mixture as a whole and selective for the aromatic componentof said mixture, and being selected from that group of such compoundswhich consists of (l) compounds containing a single vhydroxyl group inthe molecule and (2) compounds containing two hydroxyl groups and atleast one ether group in the molecule; while the secondary solventcompound is completely miscible with the primary but is only partiallymiscible, at most, with each of the components of said hydrocarbonmixture and-contains at least two hydroxyl groups in the molecule, saidoxygenated compounds being so proportioned in the mixed or compositesolvent that a mixture of the composite solvent with the most solublearomatic hydrocarbon to be extracted will separate into two liquodphases; separating the two liquid phases resulting from the intim-atecontacting of said composite solvent with said liquid mixture ofhydrocarbons, namely, a rafiinate phase poor in said aromatic componentand comprising most of said non-aromatic com- -ponentI and a solvent orextract phase -rich in said aromatic component; then intimatelycontacting such aromatic-rich extract phase with a more concentrated.aromatic extract product derived from a later stage of the process,thereby producing an extract phasevricher in said aromatic component andpoorer in said non-aromatic component, and removing solvent from suchenriched extract phase to obtain an aromatic extract product practicallyfree of solvent; the extracting and enriching operations being performedsubstantially in the absence of water.

15. Theprocess set forth in claim 14, wherein the primary solvent isselected from the group consisting of methyl alcohol, ethyl alcohol,isopropyl alcohol, dipropylene glycol, tetraethylene glycol,hexaethylene glycol, nonaethylene glycol, and Carbowax 1500, while thesecondary solvent is a diilerent solvent selected from the groupconsisting of ethylene glycol, diethylene glycol, triethylene glycol,tetraethylene glycol, and propylele glycol.

16. The process of extracting a valuable aromatic product from a liquidmixture of hydrocarbons that has both aromatic and non-aromatichydrocarbon components, which comprises intimately contacting such ahydrocarbon mixture with mixed primary and secondary solvents comprisingdifferent aliphatic alcohols, the primary solvent being at leastpartially miscible with said hydrocarbon mixture as a whole andselective for said aromatic component, while the 'secondary .solvent isa dihydric alcohol that is completely miscible with the primary solventbut is only partially miscible. at most, with each of said hydrocarboncomponents, said alcohols being so proportioned in the mixed solvent las'to permit formation, at the temperature of operation, of separableliquid phases in a mixture of the composite solvent with the mostsoluble aromatic hydrocarbon to be extracted; separating the two phasesresulting from such intimate contacting of the hydrocarbon mixture withthe composite solvent, namely, a raffinate phase poor in said aromaticcomponent and comprising most of said non-aromatic component, and asolvent or extract phase rich in said aromatic component: thenintimately contacting such aromatic-rich extract phase with a moreconcentrated aromatic extract product derived from a later stage of theprocess, thereby producing an extract phase richer in said aromaticcomponent and poorer in said non-aromatic component, and removingsolvent from such enriched extract phase to obtain an aromatic extractproduct practically free of solvent.

17. The process set forth in claim 16, wherein the extracting andenriching operations are performed within the range of ordinarymoderatel atmospheric temperatures, and the mixed solvent issubstantially free of water.

18. The process set forth-in claim 16, wherein the extraction andenriching operations are performed within a temperature range of fromabout 70 to 90 F., and in the substantial absence of water.

19. The process set forth in claim 16, wherein the primary solvent isselected from-the group consisting f methyl alcohol, ethyl alcohol,isopropyl alcohol, dipropylene glycol, tetraethylene glycol,hexaethylene glycol, nonaethylene glycol and Carbowax 1500, while thesecondary solvent is a different solvent selected from the groupconsisting of ethylene glycol,` diethylene glycol, triethylene glycol,tetraethylene glycol, andpropylene glycol,

20. The process set forth in claim 16, wherein both the primary solventand the secondary solvent are glycols, and the extraction is performedwithin a temperature range of from about 70 to 90 F., in the substantialabsence of water.

21. The process set forth in claim 16, wherein the mixed solventconsists of dipropylene glycol and ethylene glycol.

22. The process setV forth in claim 16. wherein the mixed solventconsists of approximately 65% dipropylene glycol and 35% ethyleneglycol, by weight.

23. The process set forth in claim 16, wherein the mixed solventconsists of approximately 65% dipropylene glycol and 35% ethyleneglycol, by weight, and the extracting and enriching operations areperformed within a temperature range of from about 70 to 90 F., in thesubstantial absence 0f Water.

24. The process set forth in claim 16, wherein the mixed solventconsists of methanol and ethylene glycol- 25. The process set forth inclaim 16. wherein the mixed solvent consists of approximately 70%methanol and 30% ethylene glycol, by weight.

26. The process set forth in claim 16. wherein the mixed solventconsists of approximately 70% methanol and 30% ethylene glycol. byweight.

and the extracting and enriching operations are performed within atemperature range of from about 70 to 90 F., in the substantial absenceof water.

27. 'I'he process set forth in claim 1, further characterized by thefact that the extraction is effected by continuous countercurrentcontacting of a solvent phase with a hydrocarbon phase.

28. The process set forth in claim 1. further characterized by the factthat the extraction is effected by continuous countercurrent contactingof a continuous solvent phase with a disperse hydrocarbon phase.

29. The process set forth in claim 2. further characterized by the factthat the extraction is effected by continuous countercurrent contactingof a solvent phase with a hydrocarbon phase.

30. The process set forth in claim 3, further characterized by the factthat the extraction is effected by continuous countercurrent contactingof a solvent phase with a hydrocarbon phase.

31. The process set forth in claim 3, wherein the primary solvent isselected from the group consisting of methyl alcohol. ethyl alcohol,isopropyl alcohol, dipropylene glycol, tetraethylene glycol,hexaethylene glycol, nonaethylene glycol and Carbowax 1500," while thesecondary solvent is a different solvent selected from the groupconsisting of ethylene glycol, diethylene glycol, triethylene glycol,tetraethylene glycol, and propylene glycol; the extraction beingeffected within a temperature range of from about to 100 F. and in thesubstantial absence of water, by continuous countercurrent contacting ofa solvent phase with a hydrocarbon phase.

32. The process set forth in claim 3, wherein the mixed solvent consistsof dipropylene glycol and ethylene glycol, the extraction being effectedby continuous countercurrent contacting of a solvent phase with ahydrocarbon phase.

. 33. The process set forth in claim v3, wherein the mixed solventconsists of approximately diproylene glycol and 35% ethylene glycol, byweight, and the extraction is performed within a temperature range offrom about to 90 F., substantially in the absence of water, theextraction being effected by continuous countercurrent contacting of acontinuous solvent phase with a disperse hydrocarbon phase.

34. The process set forth in claim 14, further characterized by the factthat the extracting and enriching operations are effected by continuouscountercurrent contacting of the solvent phase and the hydrocarbonphase.

35. The process set forth in claim 14, further characterized by the factthat the extracting and enriching operations are effected by continuouscountercurrent contacting of the solvent in continuous phase withhydrocarbon feed in disperse phase.

36. The process set forth in claim 14, further characterized by the factthat the extracting and enriching operations are effected by continuouscountercurrent contacting of the solvent phase andthe hydrocarbon phase.

37. The process set forth in claim 16, further characterized by the factthat the extracting and enriching operations are'effected by continuouscountercurrent contacting of the solvent phase and the hydrocarbonphase.

38. The process set forth in claim 16. wherein the primary solvent isyselected from the group consisting of methyl alcohol, ethyl alcohol,isopropyl alcohol. dipropylene glycol, tetraethylene glycol,hexaethylene glycol. nonaethylene glycol and "Carbowax 1500, while thesecondary solvent is a different solvent selected from the groupconsisting of ethylene glycol, diethylene glycol. triethylene glycol,tetraethylene glycol, and propylene glycol; the extracting and enrichingoperations being effected within a range of from about 60f7 to 100 F.and in the substantial absence of water, by continuous countercurrentcontacting of the solvent phase and the hydrocarbon phase.

39. The process set forth in claim 16, wherein the mixed solventconsists of dlpropylene glycol and ethylene glycol. the extracting andenriching operations being effected by continuous countercurrentcontacting of the solvent phase and the hydrocarbon phase.

40. The process set forth in claim 16, wherein the mixed solventconsists of approximately 65% dipropylene glycol and 35% ethyleneglycol, by weight, and the extracting and enriching operations areperformed within a temperature range of from about 70 to 90 F., in thesubstantial absence of water, the extracting and enriching operationsbeing effected by continuous countercurrent contacting of the solvent incontinuous phase with hydrocarbon feed in disperse phase.

41. The process Vof extracting a valuable aromatic product from amineral o il distillate containing. a substantial percentage ofaromatics, which comprises continuously feeding said distillate into anextraction column at an intermediate level, and at the same timecontinuously introducing into said column at a suitably higher level amixed solvent consisting of dipropylene glycol and ethylene glycol inproportions, by weight, withinthe range of from 25%-80% diproplyeneglycol to 75%20% ethylene glycol, in such manner that the resultantsolvent and hydrocarbon phases travel countercurrently in intimatemutual contact, leading away a solvent- Door raiiinate of low aromaticcontent from the column at a level above that of solvent introduction,continuously introducing into the column at a level substantially belowthat of feed introduction a liquid reuxlricher in aromatics than thesolvent phase at the feed level, withdrawing extract solution enrichedin aromatics from the column at a level below the reflux inlet, whilemaintaining a separation interface between the two phases at apredetermined constant level in the column by properly coordinating therates at which the several liquids enter and leave the co1- umn,utilizing a part of said extract solution, after at least partialseparation of solvent therefrom, to supply the reflux aforesaid, andseparating solvent from the remainder to obtain a concentrated aromaticextract product.

42. 'Ihe process set forth in claim 4l, wherein the mixed solventconsists, approximately, of 65% dipropylene glycol and 35% ethyleneglycol and is employed in continuous phase, while the mineral oildistillate constituting the feed is in disperse phase, and theconstant-level separation interface in maintained at a level betweenthatY of solvent introduction and that of raflinate withdrawal. l

43. The process set forth in claim 41 which further includes separatingmost of the solvent for re-use by distilling overhead from the-Withdrawnextract solution under reduced pressure substantially all the extractedmatter and water contained therein, together with a small proportion ofthe solvent, leaving the mixed glycolsv solvent as a virtuallywater-free residuum.

44. The process set forth in claim 41. which furtherA includesseparating most of the solvent cols are distilled overhead, leaving saidimpurities as a residuum.

45. The process set forth in claim 4l, wherein the mixed solventconsists, approximately, of dipropylene glycol and 35% ethylene glycoland is employed in continuous phase, while the mineral oil distillateconstituting the feed is in disperse phase, and the constant-levelseparation interface is maintained at a level between that ot solventintroduction andy that of raiilnate withdrawal; which further includesseparating most \oi the solvent for re-use by distilling overhead fromthe withdrawn extract solution under reduced pressure substantially allthe extracted matter and water contained therein, together with a smallproportion of the solvent, leaving the mixed glycols solvent as avirtually waterfree residuum, and separating high-boiling impuritiesfrom at least a portion of said mixed glycols residuum. before re-use,by subjecting it to reduced pressure distillation wherein the glycolsare distilled overhead, leaving said impurities as a residuum.

46. 'I'he process set forth in claim 4l, which further includesseparating most of the solvent for re-use by distilling overhead fromthe withdrawn extract solution under reduced ypressure substantially allthe extracted matter and water contained therein, together with a smallproportion of the solvent, leaving the mixed glycols solvent as avirtually water-free residuum; and which further includes separatinghigh-boiling impurities from at least a portion of said mixed glycolsresiduum, before re-use, by subjecting it to reduced pressuredistillation wherein the glycols are distilled overhead, leaving saidimpurities as a residuum, water-washing the raillnate to separatetherefrom for re-use the small amount of solvent contained therein, andthen subjecting the resultant aqueous solvent to a suitable dehydratingtreatment for removal of water therefrom.

47. The process set forth in claim 41, which further includes separatingmost of the solvent for re-use by distilling overhead from the withdrawnextract solution under reduced pressure substantially all the extractedmatter and water contained therein, together with a small proportion ofthe solvent, leaving the mixed glycols solvent as a virtually water-freeresiduum; and which further includes separating high-boiling impuritiesfrom at least a portion of said mixed glycols residuum, before re-use.by subjecting it to reduced pressure distillation wherein the glycolsare. distilled overhead, leaving said impurities as a residuum,water-washing the raffinate to separate therefrom for re-use the smallamount of solvent contained therein, and then subjecting the resultantaqueous solvent to a suitable dehydrating treatment for removal of watertherefrom; water-washing the overhead 'distillate separated from theextract solution, and

l dehydrating the aqueous solvent thus recovered.

for re-use by distilling overhead. from the withdrawn extract solutionunder reduced pressure substantially all the extracted matter and watercontained therein, together with'a small proportion of the solvent,leaving the mixed glycols solvent as a virtually water-free residuum;and which further includes separating high-boiling impurities from atleast a portion of said Amixed glycols residuum, before re-use, bysubjecting it to reduced pressure distillation wherein the gly- 48. Theprocess set forth in claim 41, which further includes separating most ofthe solvent for re-use by distilling overhead from the withdrawn extractsolution under reduced pressure substantially all the extracted matterand water contained therein, together with a small proportion of thesolvent, leaving the mixed glycols solvent as a virtually water-freeresiduum; and which further includes separating high-boiling impuritiesfrom at least a portion of said mixed glycols residuum, before re-use,by subjecting it to reduced pressure distillation wherein the glycolsare distilled overhead, leaving said im puritles as a residuum,Water-washing the rafflnate to separate therefrom for re-use the smallamount of solvent contained therein. and then subjecting the resultantaqueous solvent to a suitable dehydrating treatment for removal of watertherefrom; water-washing the overhead distillate separated from theextract solution, dehydrating the aqueous solvent thus recovered, thewater previously used in washing solvent from the ralnate being employedin washing said overhead distillate.

49. The process of extracting a valuable aromatic product from a mineraloil distillate containing a substantial percentage of aromatics, whichcomprises continuously feeding said distillate into an extraction columnat an intermediate level, and at the same time continuously introducinginto said column at a suitably higher level a substantially water-freemixture of primary and secondary liquid solvents comprising differentaliphatic oxygenated polar carbon compounds; the primary solventcompound being at least partially miscible with said mineral oildistillate as a whole and selective for the aromatic content thereof,and being selected from that group of such compounds which consists of(1) compounds containing a single hydroxyl group in the molecule and (2)compounds containing two hydroxyl groups and at least one ether group inthe molecule; while the secondary solvent is completely miscible withthe primary but is only partially miscible, at most, with each of thecomponents of said distillate and contains at least two hydroxyl groupsin the molecule; said oxygenated compounds being so proportioned in themixed or composite solvent that a mixture of the composite solvent withthe most soluble aromatic hydrocarbon to be extracted will separate intotwo liquid phases; causing the resultant solvent and hydrocarbon phasesto travel a substantial distance countercurrently in intimate mutualcontact, and leading away a solvent-poor raffinate of low aromaticcontent from the column at a level above that of solvent introduction;continuously introducing into the column at a level substantially belowthat of feed introduction a liquid 26 reflux richer in aromatics thanthe solvent phase at the feed level, and withdrawing extract solutionenriched in aromatics from the column at a level below the reflux inlet.while maintaining a separation interface between the two phases in thecolumn by properly coordinating the rates at which the several liquidsenter and leave the column; utilizing a part of said extract solution,after at least partial separation of solvent therefrom, to supply thereflux aforesaid. and separating solvent from the remainder to obtain aconcentrated aromatic extract product.

50. The process set forth ln claim 49, wherein the mixture of primary.and secondary liquid solvents comprises different aliphatic alcohols,the secondary solvent being a dihydric alcohol.

51. The process set forth in claim 49, wherein both the primary solventand the secondary solvent are glycols.

ALLEN S. SMITH.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS.

Number Name Date 2,056,830 Coleman et al. Oct. 6, 1926 2,081,719 VanDijck May 25, 1937 2,091,078 McKittrick et al. Aug. 24, 1937 2,101,643Engelke Dec. 7, 1937 2,215,915 Cope et al. Sept. 24, 1940 2,241,430 SnowMay 13, 1941 2,243,873 Lyman June 3, 1941 2,246,297 Duncan et al June17, 1941 2,302,383 Stratford et al Nom-17. 1942 FOREIGN PATENTS NumberCountry Date 96,701 Hungary Oct. 1, 1929 336,945 Great Britain Oct. 20,1930 439,674 Great Britain Dec. 11, 1935 456,958 Great Britain Nov. 18,1936 OTHER REFERENCES Petroleum Review and Mining News, Oct. 17, 1903,page 31o. (Article by Kharithkoir.)

